A procedure has been developed for preparation of an affinity column suitable for rapid (less than 0.5h) purification of rabbit antibenzodiazepine antibodies. The antibodies can be obtained from the column directly suitable for iodoimmunoassay simply by neutralizing the appropriate fraction of column effluent. The first irreversible ligands specific for kidney and brain "peripheral" benzodiazepine receptors (to the exclusion of the "central" receptor) have been synthesized and identified biochemically. These compounds are isothiocyanate derivatives of Ro 54864 and PK 11195 and promise to be of enormous value in elucidation of the structure and physiologic function of the peripheral benzodiazepine receptors. Investigations along these lines are now in progress and will be reported in due course.